1. Field of the Invention
This invention relates to a pneumatically powered, hand held or spindle-mounted lightweight tool suitable for grinding and polishing and, more particularly, to a turbine rotor for a lightweight, grinding tool driven by an air-powered reaction turbine. The turbine rotor creates high torque for a drive shaft without a significant increase in size or weight of the grinding tool.
2. Description of Related Art
In the prior art, lightweight pneumatic tools have been used for a variety of functions, such as grinding, polishing, metal or plastic finishing, engraving, drilling, and deburring. The tool variations include hand-held and machine spindle-mounted embodiments. Hand-held tools often include a narrow cylindrical exterior housing that includes a handle portion enclosing the rotor and a drive shaft that is held much like a pencil or pen. Lightweight pneumatic grinding tools can be hand held for longer periods of time than a comparable electric motor tool which is much heavier without harm to the user.
Prior art pneumatically-powered tools utilize either a vane-type fluid motor or a reactive rotor. The present invention does not employ a vane-type motor but utilizes a reactive rotor. The reactive rotor expels high pressure, high velocity air tangentially from the rotor peripherally to obtain torque. The rotor is coupled to the primary drive shaft therein.
U.S. Pat. No. 5,566,770, which has a common assignee with the present invention, provides an angled spindle that is relatively lightweight driven by a single chamber rotor. U.S. Pat. No. 4,776,752, which also has a common assignee with the present invention, teaches a single chamber turbine rotor that is relatively lightweight and includes a high-speed governor.
Although the torque provided in current turbine rotors is adequate for grinding and polishing tools that are lightweight and compact, higher torque in some applications of grinding and polishing is desirable. However, enlarging the tool rotor (and therefore the housing) to increase torque could greatly increase the weight, size and volume of the tool housing and therefore reduce the hand-held, lightweight advantages of the tool.
The present invention increases the torque of a rotor driven pneumatic tool significantly without concomitant increases in weight, size or complexity of operation or manufacture of the tool. In fact, an increase in torque becomes possible with a decrease in diameter of the tool. For example, where a rotor approximately one inch in diameter would provide approximately 0.2 horsepower at 50,000 revolutions per minute (“RPMs”), with the present invention a rotor of only ¾ inch in diameter provides approximately 0.3 horsepower at 50,000 RPMs. In addition to an increase in power, the present invention provides for a slimmer tool profile. Moreover, the present invention also reduces the pressure that is necessary to idle the rotor in comparison to a single rotor of comparable size and material from three cubic feet per minute for the one inch single rotor to two cubic feet per minute for a ¾ inch dual rotor.
The present invention uses a rotor comprising a single, compact body having dual, high pressure air receiving chambers that share a common wall, to reduce size and weight for increased torque. Both rotor body chambers have tangential exhaust nozzles that generate torque to rotate the rotor. The present invention may also include dual automatic speed governors without additional complexity.
A lightweight tool is also desirable in a spindle mount since the tool is supported on a moveable arm.